Traditional alternating current (AC) circuit breakers employ electro-mechanical means to provide protection against current overload and inrush. Similarly, alternating current (AC) circuit breakers employing electronic circuits to detect and trip the breakers when ground faults and/or arc faults are detected also generally incorporate an electro-mechanical means to provide protection against current overload and inrush. In these circuit breakers the electronics generally do not provide monitoring or protective control of the breaker in regard to current overload or inrush. Thus, should the electronic circuitry protecting against ground fault and/or arc fault fail, the breaker will still maintain its protection against overload and excessive inrush current.
Ideally, such a circuit breaker would also be able to employ electronic circuitry, either solely or combined with ground-fault and/or arc fault protection, to monitor current overload and inrush current and thereby trip the breaker should either be excessive. The electronics therein would be able to be exactingly programmed to provide precise protection against overload and inrush current. The problem with only employing electronic circuitry to provide a breaker's protective capability has been that, should the electronic circuitry fail, the breaker could remain in an “on” (connected) status during an overload, resulting in a dangerous, unacceptable condition.
An electro-mechanical circuit breaker that employs either thermal bi-metal construction, or hydraulic-magnetic construction, to provide current overload and inrush protection, is not completely failure proof, but is designed to be as failure proof as possible. Thus, any design of an electronically controlled circuit breaker would necessitate a similar degree of failure proof construction as inherent within traditional electro-mechanical circuit breaker designs.
Safety becomes a major factor in any employment of AC electronic circuit breakers that rely totally on solid-state microprocessor controlled electronics to provide protection without the incorporation of a physical contact opening during a trip (i.e., off) state. Also, existing technology for circuit protection that solely employs solid-state microprocessor controlled electronics to switch high voltage AC power incurs high cost and significant heat dissipation problems. The most practical and safe approach is to combine microprocessor based electronics to monitor the desired circuit protection parameters with a mechanical contact mechanism that would provide a physical contact gap in the open (i.e., off) position.
Attempts have been made to provide AC electronic circuit breakers that rely totally on solid-state microprocessor controlled electronics to provide protection against current overload and inrush current in addition to ground-fault and/or arc fault protection. However, none of these attempts have resulted in a circuit breaker design that provides a similar degree of failure proof construction as inherent within traditional electro-mechanical circuit breaker designs.
For example, U.S. Pat. No. 4,331,999 to Engel et al. and U.S. Pat. No. 4,338,647 to Wilson et al. disclose circuit interrupters with a digital control unit (154) that causes tripping of a trip coil (22) in response to various sensed conditions. However, both references discuss the use of a switching field effect transistor (192) to control the flow of current through the trip coil (22) in response to signals from the digital control unit (154). As such, in the case of failure within the digital control unit (154) and/or the transistor (192), the transistor (192) may be stuck in the unenergized state, thereby rendering the trip coil (22) inoperative, resulting in a potentially dangerous condition.
As such, there remains an unmet need in the industry for an electronically controlled circuit breaker that incorporates a mechanical contact mechanism while maximizing the fail-safe level of the breaker to insure its ability to provide the required circuit protection.